Thin films offer a means of modifying the surface of a material whilst retaining the bulk properties of a material. We have a wide range of techniques for depositing thin film materials.

> Sputter Deposition

Sputtering is flexible deposition method with non reactive processes for depositing materials from a target of the same material. DC sputtering is confined to materials with significant electrical conductivity and rf sputtering is useful for both conductive and non conductive materials. Reactive processes allow the formation of compound materials by admitting some constituents from the gas phase in order to combine them with the target material.

> Electron Beam evaporation

An electron beam is used to evaporate material from a copper hearth. The method is able to deposit a wide range of materials and gives high deposition rates if required. We have the additional capability of depositing two materials simultaneously from two separate sources.

> Plasma Enhanced Chemical Vapour Deposition (PECVD)

In this technique a plasma is used to produce condensable species from suitable feedstock gases. The species condense on the substrate to produce a coating. We have developed this technique into a commercial method of depositing multiplayer coatings under computer control with the assistance of a SPIRT grant. Our commercial partner in this work, Avtronics Ltd has installed plant to do commercial coating work using PECVD, based on the silicon oxynitride system of materials

> Cathodic Arc Deposition

The Cathodic arc is an intense source of highly ionised plasma ideal for depositing materials onto surfaces, and under some conditions, implanting these materials into a surface. Research is under way into the basic physics and applications of cathodic arcs. An amazing fact is that the temperature of the bright spot on the cathode surface, which is the source of the ionised material, is in excess of 40,000 degrees. The almost fully ionised plasma may be guided by magnetic fields which results in the formation of a beam of this plasma material. This has resulted in a fascinating area of plasma physics concerned with the behaviour of these plasmas being opened up. The photograph below shows fully ionised plasma streaming through a mask.

We have two deposition systems for carrying out filtered arc deposition of materials, and a new system under construction for carrying out pulsed deposition from multiple sources. Cathodic arc deposition has advantages over other methods of deposition: the plasma produced by the arc source is highly ionised and therefore it is possible to combine the technique with ion implantation methods such as PIII. The rate of deposition is very high and so the influence of the background vacuum on film purity is less.